1. Field of the Invention
The present invention relates to the field of electromagnetic actuators which produce alternating movement.
2. Discussion of the Background
Such actuators are provided in known manner with a central pole and two lateral poles. The central pole supports an exciting coil as well as a mobile portion equipped with thin permanent magnets magnetized along the direction of the air gap. German Patent DE 2603681 describes such an actuator. This actuator is provided with a fixed coil which generates an alternating flux and with two mobile magnets which are displaced in opposite senses. The electromagnetic phenomena involved obey Laplace's law (flux passing through the coil due to magnets). The magnets are not pairs of thin magnets attached to one another in opposite senses, but are two magnetic bars, each interacting with the magnetic flux created by the coil.
Such a prior art actuator suffers from major disadvantages: the structure obeying Laplace's law does not guarantee linearity of the relationship between force and the current supplying the coil. Furthermore, the efficiency of such actuators, or in other words the force per applied watt, is low. The lack of linearity leads to operating irregularity, and makes it necessary to provide complex automatic control electronics to remedy such linearity defects.
A solution to this general problem was provided by the Applicant in the form of European Patent EP 93910083.0, which describes an actuator exhibiting three stator poles and a single coil surrounding the central pole. This solution comprises using a fundamentally different electromagnetic structure, which does not obey LAPLACE's law. The proposed structure is provided with two pairs of thin magnets, which are attached to one another in alternating senses and which are displaced in an air gap.
It has become apparent with prior art devices that the vibration frequency of the mobile member is limited. As soon as the frequency is increased, the force delivered per unit of electrical power dissipated decreases, thus limiting the performances of the actuator constructed by application of European Patent EP 93910083.0. The objective of the invention is to extend the limits of vibrational frequencies by proposing a structure capable of increasing the electromagnetic efficiency.